1. Field of the Invention
The present invention relates to an apparatus for and a method of recording an image on a recording medium.
2. Description of the Background Art
In the step of printing, a plurality of unit images are superimposed on each other to form a single objective image in some cases. Examples of the plurality of unit images include single-color images for cyan, magenta, yellow and black. An image recording apparatus for forming printing plates corresponding to the respective unit images is used in such a printing step.
The image recording apparatus employs a deflector such as a polygon mirror to move an optical beam such as a laser beam in a main scanning direction, and moves a printing plate in a sub-scanning direction. In this manner, the image recording apparatus forms a two-dimensional image on the printing plate. This two-dimensional image is a unit image. The image recording apparatus produces a plurality of such unit images. Then, a known printing machine overprints these unit images on a sheet of paper to form a color image. This color image is an objective image.
FIG. 15 shows a construction of a conventional image recording apparatus 500. An optical beam emitted from a light source 510 is deflected in the main scanning direction by a deflector 520. The deflected optical beam passes through an image-forming optical system 530, and is imaged on a recording surface of a printing plate 540. Thus, an image is recorded.
However, if there is a defective spot 531 such as flaws, striae and the like in part of an optical member constituting the image-forming optical system 530, the intensity of the optical beam is attenuated when the optical beam passes through the defective spot 531. This causes a partial decrease in the density of each main scanning line 560 on the printing plate 540, resulting in the appearance of a lightly colored streak 570 in the recorded image.
After the production of a plurality of printing plates in such an image recording apparatus 500, the images recorded on the respective printing plates include streaks 570 in the same position. For example, when printing plates for yellow, magenta, cyan and black are produced, the images recorded on the respective printing plates include streaks y, m, c and k in the same position, as shown in FIG. 16. When these images are overprinted on a single sheet S, the streaks y, m, c and k are superimposed on each other, thereby to be intensified. This results in the appearance of a conspicuous streak X in the color image formed on the sheet S.